Within the field of cutting tools used in rotary machining operations, there are many examples of tool holders having insert receiving pockets with stress relief surfaces. Stress relief surfaces are typically located between a support surface and an abutment surface of the insert receiving pocket to reduce the tensile and compressive stresses exerted on the tool holder, via a removably secured cutting insert, during machining operations.
Reference can be made to FIGS. 8 to 10 of U.S. Pat. No. 6,929,427 and FIGS. 1 and 7 of U.S. Pat. No. 8,506,208 for prior art examples of tool holders having insert receiving pockets with stress relief surfaces.
Finite element analysis (FEA) of the tensile stresses exerted on insert receiving pockets having stress relief surfaces, has shown that peak stress values occur at or adjacent the corner intersection of the stress relief surfaces and adjacent pocket peripheral surfaces, and this also applies for insert receiving pockets configured with corner intersection surfaces having a chamfer or a concave shape when viewed in cross-section.
FIGS. 1 to 3 show an insert receiving pocket 124 according to the prior art, configured with a corner intersection surface 134, between a first stress relief surface 130 and an adjacent pocket peripheral surface 132. As seen in FIG. 4, the corner intersection surface 134, which essentially serves as a second relief surface, has a concave shape when viewed in cross-section.
As also seen in FIG. 4, in cross-section, the corner intersection surface 134 extends between a first endpoint 136 and a second endpoint 138. At its first endpoint 136 the corner intersection surface 134 forms a first discontinuity with the adjoining first stress relief surface 130, and at its second endpoint 138 the corner intersection surface 134 forms a second discontinuity with the adjoining pocket peripheral surface 132.
FIG. 5 is an FEA diagram showing the tensile stresses exerted on the insert receiving pocket 124, via a removably secured cutting insert (not shown), during cutting operations, with a peak tensile stress value of 37 Kgf/mm2 occurring immediately adjacent the corner intersection surface 134.